Method for applying a thermoplastic locking patch on a threaded fastener

ABSTRACT

A finely powdered thermoplastic material is placed in a fluidizing chamber and is dispensed on a preheated threaded fastener element in controlled amounts by controlled air pulsations which pass through a venturi tube arrangement. The powdered material is deposited on the threaded surface in a predetermined amount and is fused thereto to provide a locking patch of solidified thermoplastic material.

ilnited States Patent [191 1111 3,720,533 Gallagher 1 51Marcl1 13, 1973 54] METHOD FOR APPLYING A 3,294,139 12/1966 Preziosi ..151/7 THERMOPLASTIC LOCKING PATCH 3,416,492 12/1968 Greenleafi. ....1 18/308 ON A THREADED FASTENER 3,530,827 9/1970 Burke ..1 18/308 Inventor: James J. Gallagher, Chalfont, Pa.

Standard Pressed Steel Co., Jenkintown, Pa.

Filed: Jan. 12, 1971 Appl. No.2 105,936

Assignee:

US. Cl. ..ll7/2l, 117/25, 117/37, 117/49, 117/132 C, 118/308, 151/7 Int. Cl. ..B44d l/094 Field of Search ..1 17/16, 21, 25; 118/308; 151/7 References Cited UNITED STATES PATENTS 3/1970 Duffy ..151/7 Primary ExaminerMurray Katz Attorney- Stanley Belsky et a1.

[57] ABSTRACT A finely powdered thermoplastic material is placed in a fluidizing chamber and is dispensed on a preheated threaded fastener element in controlled amounts by controlled air pulsations which pass through a venturi tube arrangement. The powdered material is deposited on the threaded surface in a predetermined amount and is fused thereto to provide a locking patch of solidified thermoplastic material.

5 Claims, 3 Drawing Figures PATENTEUHARIBIQYS ,53

- l mu \\\\Ql INVEN JAMES J. GALL ER METHOD FOR APPLYING A THERMOPLASTIC LOCKING PATCH ON A THREADED FASTENER This application is a division of application Ser. No. 741,466, filed July 1, 1968, and now U.S. Pat. No. 3,557,750.

This invention relates to an apparatus and method for making self-locking threaded fasteners of the type having a locking patch of thermoplastic resin bonded to the undistorted thread surfaces. Self-locking threaded fasteners of the type having a locking patch of thermoplastic resin bonded to the thread surfaces have found wide commercial application. This widening commercial demand requires a manufacturing technique which allows a volume production in a rapid and economically feasible manner while maintaining high standards of quality for the finished product. U.S. Pat. No. 3,294,139 to Preziosi discloses a recent attempt at solving this problem wherein a measured quantity of powdered thermoplastic resin is placed on the thread surface of a fastener and heat is applied to melt the powder into a free-form liquid pool which is allowed to cool and solidify in such shape without deformation from extraneous pressures. This method has a number of manifest disadvantages including the difficulty of controlling the volume of powdered resin applied to the fastener and of directing the powder to, and confining it within, the desired area on the threaded surface. Examination of fasteners which have been produced employing this process under actual commercial conditions reveals wide variations in the size and shape of the resin patches, many having an uneven lumpy surface, or even a spattered appearance with portions of the resin being in the form of small droplets separate from the main resin body.

It is therefore among the objects of this invention to provide a novel method and apparatus to produce threaded fastener elements having a locking patch of thermoplastic resin bonded to the thread surfaces in a rapid, economically feasible manner. It is also among the objects of this invention to provide a method and apparatus for producing such threaded fastener elements wherein the volume of thermoplastic material applied to the threaded surfaces can be carefully and precisely controlled in order to insure uniform products. A still further object of the present invention is to provide a method and apparatus for producing such fastener elements wherein the locking patch of thermoplastic material is uniformly bonded to the thread surfaces to provide a strong bond so that shearing forces, applied during use of the fastener element, will not cause a rupture of the bond between the resin body and the thread surfaces and an impairment of the locking function.

In the drawing:

FIG. 1 is a schematic representation of the apparatus of the present invention;

FIG. 2 is a horizontal, sectional view taken on line 2-2 of FIG. 1; and

FIG. 3 is a detailed vertical section showing an alternate embodiment of the present invention adapted for female fastener elements.

Referring now to the drawing, particularly FIGS. 1 and 2, a fastener element having a threaded shank 12 is shown carried by a rotating indexing table 14. The table 14 includes a central support shaft 15 and a plurality of circumferentially spaced bolt retaining stations 16 which hold and retain the bolts in a vertical position. The table 14 is incrementally indexable and, as it indexes, the bolts 10 in the circumferentially spaced retaining stations 16 are first heated in an inductance heating unit (not shown) to a temperature of 250 to 700 F. and then carried to a patch applying station 18 where the powdered thermoplastic resin, for example a polyamide (nylon) is applied.

Station 18 includes a pair of jaw chucks 20 and 22, respectively, each having a half-cylindrical channel 24 and 26, respectively, which, when the chucks 20 and 22 are in abutting relationship, define a cylindrical bolt shank receiving cavity 28 closely confining the threaded shank 12 of the bolt. The jaws 20 and 22 are selectively movable from a spaced apart relationship wherein, as table 14 indexes a bolt 10 to the station, the bolt is allowed to pass between the spaced jaw chucks, to a closed position, shown in FIG. 2, wherein the bolt is confined within the cavity 28.

The thermoplastic material which is to be deposited on a bolt shank 12 is stored, in finely powdered form, in a fluidizing chamber 30 where the powder, shown at 32, is maintained in an agitated and fluidized state by a forced circulation of air from air line 34 in the lower portion of chamber 30. The air passes through a porous membrane 35 which separates the upper portion 36 of chamber 30 from the air entry chamber 37. The air vibrator 38 in lower chamber 37 disperses the stream of air entering through line 34 so that it circulates uniformly and passes through membrane 35 to uniformly agitate and fluidize the finely divided particles of thermoplastic material 32.

A tube 40 communicating with the upper chamber 36 directs the fluidized thermoplastic material from the chamber 36 to a powder delivery system 42 which in turn directs the thermoplastic material to the bolt shank 12, as will be explained more fully hereinbelow. Delivery system 42 includes an initial air flow line 44 from a pressurized air supply (not shown) which passes the air through a pulsating air valve 46 designed to allow discrete pulses of air from line 44 to pass through at predetermined timed intervals and in a predetermined volume. The pulsating air from the discharge of valve 46 enters discharge line 48 which leads to a venturi nozzle 50 and from there through delivery tube 52 to the bolt shank 12. Delivery tube 52 is housed in an aperture 54 in jaw chuck 22 and is pinched, as at 56, into a substantially elliptical shape in order to deliver the thermoplastic powdered material in a vertically elongated pattern on the bolt shank 12.

Tube 40 intersects the venturi nozzle at the throat 58 where, as the pulsating air stream approaches the throat, the velocity increases and the throat pressure decreases. The decrease in throat pressure creates a partial vacuum effect which sucks up a portion of the fluidized powdered thermoplastic material and entrains this material in the air stream to be delivered through line 52 to the bolt shank 12. The duration of the air pulse and the volume of pulsed air is carefully controlled in order to accurately control the volume of powdered thermoplastic material entrained.

The shape of the delivery section 56 and the clearance 60 (see FIG. 2) are selected to be compatible with the precisely metered amount of fluidized thermoplastic material delivered by each pulsation so that the dispersal of the powdered material on the bolt shank 12 is uniformly tapered from a minimum thickness at the edges to a maximum thickness at the center. As the pulsating blast of carrier air impinges on the bolt shank, the powdered thermoplastic material entrained therein disperses slightly outwardly from the exit tube 56 so that while the main concentration of the powdered material is directed toward the bolt shank 12, in the area immediately opposite the longitudinal central portion of the elliptical delivery tube 52, the dispersal of the carrier air outward from delivery tube 52 carries a portion of the thermoplastic material away from the longitudinal central concentration so that the patch of thermoplastic material ultimately includes a peripheral edge of minimum concentration building up toward a more highly concentrated central portion. Thus, when the bolt is in use and engages a female threaded fastener element, the bite of the initial engagement of the patch with the roots of the female threaded fastener element does not dislodge the thermoplastic material bonded to the bolt shank. Engagement is gradual and avoids excessive initial shearing forces which may tend to rupture the bond of thermoplastic material with the bolt shank.

FIG. 3 shows an alternate embodiment of the present invention wherein the fluidized thermoplastic material is directed to impinge on the thread surface of a female threaded fastener. In this embodiment, the female threaded fastener elements or nuts 60 are carried in spaced retaining trays 62 on an indexing table 140 which is incrementally indexable to a thermoplastic depositing station 64. A delivery tube 52a from a fluidizing chamber and venturi nozzle, as described above, is positioned parallel to, and just above, the nut 60 on the indexing table 14a.

The delivery segment 56a is downwardly inclined so that when a nut 60 is in the depositing station 64 the outlet portion 66 of the delivery tube 56a is adjacent the threaded surfaces of the nut. The indexing table 140 is provided with a camming mechanism (not shown) to elevate the table each time a nut 60 is in the depositing station 64. Once the charge of fluidized powder has been deposited on the nut 60 by the pulsating air stream, the table drops, indexes another nut into the station, and is elevated by the camming mechanism to put the next nut adjacent the delivery system. It is to be understood that other nut elevating devices can be employed, for example a piston immediately below depositing station 64 can selectively elevate each nut 60 in the depositing station prior to the pulse of fastener element. The volume of thermoplastic material deposited on the threaded surfaces is precisely controlled and is uniformly dispersed upon the threaded surfaces and fused thereto in such manner as to create evenly contoured and uniform patches. The process is particularly adaptable to high speed production line applications and results in products of uniformly high quality.

The specific embodiments detailed herein are by way of illustration only and are not intended to be exhaustive, as those skilled in the art may adapt the teachings of the present invention in other embodiments each as may be best suited for their particular purposes.

What is claimed is:

1. A process for applying a locking patch of thermoplastic material to the thread surface of threaded fastener elements comprising:

heating said threaded fastener elements and transporting said heated fastener elements to a thermoplastic application station;

fluidizing finely powdered thermoplastic material;

pulsating a carrier fluid so that discrete pulses of said fluid are formed and entraining a predetermined quantity of said fluidized thermoplastic material in each of said pulses;

directing said pulses to said thermoplastic applica tion station in intervals such that each pulse impinges on the thread surface of one of said heated fastener elements whereby said quantity of thermoplastic material is fusion bonded to said surface.

2. The process as defined in claim 1 wherein said carrier fluid is pulsed by drawing said stream of carrier fluid from a pressurized supply through a pulsating fluid valve thereby to accurately meter a predetermined volume of carrier fluid to control the quantity of thermoplastic material entrained.

3. The process as defined in claim 2 wherein said finely powdered thermoplastic material is fluidized in a fluidizing chamber.

4. The process as defined in claim 3 wherein said carrier fluid is a gas and said process includes the steps of directing said carrier gas through a venturi nozzle and providing a fluid communication passage from said fluidizing chamber to the throat of said venturi nozzle whereby when said carrier gas is pulsed through said venturi nozzle the pressure drop at said throat creates a partial vacuum which sucks up said predetermined quantity of thermoplastic material into said venturi nozzle thereby entraining said thermoplastic material into the pulsating stream of carrier gas.

5. The process as defined in claim 1 wherein each of said pulses is directed through a tube terminating in a portion having a generally elliptical cross-section the major axis of which is generally parallel to the axis of said thread surface whereby said quantity of thermoplastic material forms a generally elongated patch on said thread surface. 

1. A process for applying a locking patch of thermoplastic material to the thread surface of threaded fastener elements comprising: heating said threaded fastener elements and transporting said heated fastener elements to a thermoplastic application station; fluidizing finely powdered thermoplastic material; pulsating a carrier fluid so that discrete pulses of said fluid are formed and entraining a predetermined quantity of said fluidized thermoplastic material in each of said pulses; directing said pulses to said thermoplastic application station in intervals such that each pulse impinges on the thread surface of one of said heated fastener elements whereby said quantity of thermoplastic material is fusion bonded to said surface.
 2. The process as defined in claim 1 wherein said carrier fluid is pulsed by drawing said stream of carrier fluid from a pressurized supply through a pulsating fluid valve thereby to accurately meter a predetermined volume of carrier fluid to control the quantity of thermoplastic material entrained.
 3. The process as defined in claim 2 wherein said finely powdered thermoplastic material is fluidized in a fluidizing chamber.
 4. The process as defined in claim 3 wherein said carrier fluid is a gas and said process includes the steps of directing said carrier gas through a venturi nozzle and providing a fluid communication passage from said fluidizing chamber to the throat of said venturi nozzle whereby when said carrier gas is pulsed through said venturi nozzle the pressure drop at said throat creates a partial vacuum which sucks up said predetermined quantity of thermoplastic material into said venturi nozzle thereby entraining said thermoplastic material into the pulsating stream of carrier gas. 